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Definition of Pka

Pka Definition from Science & Technology Dictionaries & Glossaries
General Chemistry Glossary
(pKa) Compare with acid dissociation constant .The pKa of an acid is minus the base-10 log of its acid dissociation constant , pKa = - log Ka. For example, a pKa of 5 is equivalent to an acid dissociation constant of 10-5.
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Pka Definition from Computer & Internet Dictionaries & Glossaries
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Pka Definition from Encyclopedia Dictionaries & Glossaries
Wikipedia English - The Free Encyclopedia
PKA, pKa, or other similar variations may stand for:

  • pKa, the symbol for the acid dissociation constant at logarithmic scale
  • Protein kinase A, a class of cAMP-dependent enzymes
  • Pi Kappa Alpha, the North-American social fraternity
  • Public key authentication, establishing key authenticity in public-key cryptography 
  • Professional Karate Association
  • Primary knock-on atom
  • Professionally known as
  • Russian Federal Space Agency (
  • Painkiller Already

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An acid dissociation constant, Ka, (also known as acidity constant, or acid-ionization constant) is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction known as dissociation in the context of acid-base reactions. The equilibrium can be written symbolically as:

where HA is a generic acid that dissociates by splitting into A-, known as the conjugate base of the acid, and the hydrogen ion or proton, H+, which, in the case of aqueous solutions, exists as the hydronium ion—in other words, a solvated proton. In the example shown in the figure, HA represents acetic acid, and A- represents the acetate ion, the conjugate base. The chemical species HA, A- and H+ are said to be in equilibrium when their concentrations do not change with the passing of time. The dissociation constant is usually written as a quotient of the equilibrium concentrations (in mol/L), denoted by [HA], [A-] and [H+]:
Due to the many orders of magnitude spanned by Ka values, a logarithmic measure of the acid dissociation constant is more commonly used in practice. The logarithmic constant, pKa, which is equal to -log10 Ka, is sometimes also (but incorrectly) referred to as an acid dissociation constant:

The larger the value of pKa, the smaller the extent of dissociation at any given pH (see Henderson–Hasselbalch equation)—that is, the weaker the acid. A weak acid has a pKa value in the approximate range -2 to 12 in water. Acids with a pKa value of less than about -2 are said to be strong acids; a strong acid is almost completely dissociated in aqueous solution, to the extent that the concentration of the undissociated acid becomes undetectable. pKa values for strong acids can, however, be estimated by theoretical means or by extrapolating from measurements in non-aqueous solvents in which the dissociation constant is smaller, such as acetonitrile and dimethylsulfoxide.

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Pi Kappa Alpha (ΠΚΑ) is a North American Greek letter college fraternity which was founded in 1868. The fraternity has over 220 chapters and colonies with 14,000 undergraduate members and 250,000 lifetime initiates. Pi Kappa Alpha was originally a whites-only Southern organization, but became a national fraternity in 1909, and removed its racial restrictions in 1964.

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